only sort on order, SchemaNode is not comparable

fixes #279

CHANGES.rst

@@ -4,6 +4,9 @@ unreleased
 - Allow deferred schema nodes.
   See https://github.com/Pylons/colander/pull/280
 
+- Fix an issue when using a node multiple times in a schema by cloning it.
+  See https://github.com/Pylons/colander/issues/279
+
 1.3.1 (2016-05-23)
 ==================
 

colander/__init__.py

@@ -2242,7 +2242,7 @@ class _SchemaMeta(type):
                     value.title = name.replace('_', ' ').title()
                 nodes.append((value._order, value))
 
-        nodes.sort()
+        nodes.sort(key=lambda n: n[0])
         cls.__class_schema_nodes__ = [ n[1] for n in nodes ]
 
         # Combine all attrs from this class and its _SchemaNode superclasses.

colander/tests/test_colander.py

@@ -3403,6 +3403,17 @@ class TestSchema(unittest.TestCase):
         self.assertEqual(schema.schema_type, colander.Mapping)
         self.assertEqual(schema.children[0], node)
 
+    def test_schema_with_cloned_nodes(self):
+        import colander
+        test_node = colander.SchemaNode(colander.String())
+        class TestSchema(colander.Schema):
+            a = test_node.clone()
+            b = test_node.clone()
+        node = TestSchema()
+        expected = {'a': 'foo', 'b': 'bar'}
+        result = node.serialize(expected)
+        self.assertEqual(result, expected)
+
 class TestSequenceSchema(unittest.TestCase):
     def test_succeed(self):
         import colander